The current level of exodontia still depends on a rather primitive technique, requiring a dental elevator, a rigid tool having a thickness which is substantially greater than the thickness of a pericementum and which is pierced into the pericementum which exists between a tooth and an alveolar bone which effects a wedging action and and a leverage to dig the tooth out, thus separating the pericementum of that tooth from the alveolodental wall. Subsequently, the affected tooth is extracted by means of forceps. With such exodontology, a patient cannot bear the accompanying pain without benefit of anesthesia. The current practice of exodontia with the aid of injecting narcotic causes, in addition to creating fear in the mind of the patient concerning the injection and the pain which might be experienced during the injection, a hazard of producing medicine shocks and sequelae. When narcotic is injected, also presents a patient does not experience any pain during the operation, giving rise to the tendency that a dentist may use an external force of greater magnitude than necessary in order to extract an affected tooth. This extensively destroys the alveolodental wall or the tissues of gingiva, so whereby that the patient will suffer from inflammation after the surgical operation or suffer from sequelae that unmatured permanent teeth may be damaged. It will be therefore seen that the problems found in the art of exodontia are to enable the extraction of a tooth or teeth with little or no pain while avoiding the injection of narcotic and to minimize the destruction of the alveodental walls or tissues of gingiva.
Considering a system through which pains are transmitted during a dental operation, such system can be modelled as illustrated in FIG. 1. Specifically, a tooth 100 is covered by a cement 4 and an enamel body 11, and is secured to an alveolar bone 1 through a spring 2 having a spring constant k and a dashpot 3, both of which represent the pericementum. Dentin 5 is housed within the cement 4, and interposed between the enamel body 11 and the dentin 5 are Tomes' fibers 9 and dentinal cells/fiber cells 8, carried by tooth fluid 10 within dentinal tubules and which are supported by a group of nerve fibers of the dental pulp through another spring 6 having a spring constant K and another dashpot 7 having a viscous attenuation coefficient C. Accordingly, when the Tomes' fibers 9 and dentinal cells/fiber cells 8 are subject to a static or dynamic displacement, a strain is produced in the spring 6 of the nerve fibers of the dental pulp. The magnitude of the strain can be measured by a receiver 13 of the nerve system, which corresponds to a strain gauge. The strain can be amplified by an amplifier 15 having a certain frequency response and then recorded on a recording paper 17 associated with a recorder 16 including a pen 18. It is considered that the height of the resulting waveform is proportional to the degree of pains suffered in the dental pulp. On the other hand, a displacement of the spring 2 can be measured by a strain gauge 21 which corresponds to a group of nerves distributed in the pericementum. The magnitude of such strain may be amplified by an amplifier 14 having a certain frequency response and then recorded on the recording paper 17 by the pen 18 of the recorder 16. It is considered that the height of the resulting waveform is proportional to the degree of pains suffered by the group of nerves in the pericementum. It will be seen that this model of pain transmitting system includes a pair of channels, namely, a channel leading to the dental pulp and another leading to the group of nerves in the pericementum. The extraction of a tooth is equivalent to cutting the spring 2 which corresponds to the pericementum. In the prior art practice, the cutting operation produced large strains in the spring 6 associated with the dental pulp as well as in the spring 2 associated with the pericementum, and pains from the both channels are fed to the nerve center. However, considering the nature of resistance encountered during the exodontia, it is found that such resistance is largely due to the strength of the spring 2 associated with the pericementum, and that the influence of the strength of the spring 6 associated with the dental pulp can be neglected. Accordingly, it follows that a tooth can be easily extracted by carefully cutting the pericementum which is distributed around that tooth. The spring 2 associated with the pericementum will undergo an expansion and shrinkage in proportion to the magnitude of a pressure P applied to the tooth 100 during the exodontia, and the degree of such expansion and shrinkage causes a corresponding change in the degree of pains suffered. The injection of narcotic which is used in the prior art practice in order to alleviate pains is equivalent to disconnecting the recorder 16 from the strain guage 21 associated with the spring 2 of the pericementum, thus interrupting the transmission of a signal to the recorder 16 or the nerve center. The use of a laughing gas which is sometime used in place of narcotic is equivalent to disabling the recorder 16.